Integration of pyrolysis and anaerobic digestion – Use of aqueous liquor from digestate pyrolysis for biogas production

• Aqueous pyrolysis liquor can be digested by an un-adapted inoculum without additives.
• Up to 63.4% of COD was removed.
• Pyrolysis temperature has strong impact on degradability of pyrolysis liquor.
• Methanogenic microflora showed high adaption potential.
• VOCs were removed by large extent.

Anaerobic digestion of aqueous pyrolysis liquor derived from pyrolysis of solid digestate was tested in batch mode using an un-adapted inoculum. Three pyrolysis liquors produced at 330 °C, 430 °C and 530 °C in four COD-based concentrations of 3, 6, 12 and 30 g L−1 were investigated. The three lower concentrations showed considerable biogas production, whereas the 30 g L−1 dosage caused process inhibition. The highest methane yield of 199.1 ± 18.5 mL gCOD−1 (COD removal: 56.9 ± 5.3%) was observed for the 330 °C pyrolysis liquor, followed by the 430 °C sample with only slightly lower values. The 530 °C sample dropped to a yield of 129.3 ± 19.7 mL gCOD−1 (COD removal: 36.9 ± 5.6%). Most VOCs contained in the pyrolysis liquor (i.e. furfural, phenol, catechol, guaiacol, and levoglucosan) were reduced below detection limit (cresol by 10–60%). Consequently, integrated pyrolysis and anaerobic digestion in addition to thermochemical conversion of digestate also promises bioconversion of pyrolysis liquors.

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